Easing his beer belly from behind his SUV's wheel, my friend arrived at the restaurant for lunch. His bumper featured a "Pave the Bay" sticker, sandwiched between "People Kill People, Not Assault Rifles," and "Show Me the Birth Certificate."

On the way in, 'Pave It' chucked his extra large Styrofoam coffee cup toward a storm drain labeled "The Bay Starts Here."

Our other buddy, looking lean in spandex, carless for two years, arrived by bicycle, a "Save the Bay" sticker on his helmet next to the Peace symbol.

On the way in 'Save it' plucked the Styrofoam from the storm drain grate.

They ordered: Save It his usual double bacon burger, and Pave It his favorite chicken Caesar with a side of collards.

So which of my 'friends' (both invented just for this column), is also the Chesapeake's best friend?

Arguably, Pave It; and the reason is the very substantial role the food we eat plays in the health of coastal water bodies like our Bay.

Eating lots of meat, particularly red meat, results in far more runoff of nitrogen, a principal Bay pollutant, than Save It saves by his admirable choice to eschew driving (another big source of nitrogen to the Bay, and of climate change carbon, too).

Nor does Pave It, who has cut the beef for his own health, not from estuarine compassion, need to go vegan...just slice meat by a third to half, and shift to fish or even poultry. (As for his beer belly, beer in the diet adds virtually nothing to nitrogen pollution).

Where am I getting all this stuff? A lot of it from simply googling N-Print, featured in May's Bay Journal in Karl Blankenship's lead story: "Protein- rich diet linked to Bay's unhealthy state." Blankenship's piece should be required reading in every school of the watershed.

So should N-Print, a unique collaboration among scientists at the Universities of Virginia and Maryland, and the Netherlands. It is one of the first-ever nitrogen calculators, similar to the many carbon calculators out there.

They let you experiment with an array of lifestyle decisions, including diet, and total up the polluting nitrogen your choices produce. Another good nitrogen calculator is on the Chesapeake Bay Foundation's website.

In a nutshell, N-Print's going to show you how the average American's nitrogen "footprint" results almost 75 percent from our diets, which include nearly twice the protein our bodies need — not harmful to us, but hard on coastal waters worldwide.

The meat industry's going to tell you we get just about the needed amount of protein from meat; but that overlooks the fact that we also get protein from eggs, dairy, fish, veggies, fruit, nuts, beans and other sources.

And the production of meat-based protein is most polluting, overall, with chicken production yielding more than twice as much nitrogen as vegetables, pork about a third more than chicken, and beef two or three times more than chicken.

To its credit, U.S. agriculture has worked hard in recent decades to grow more grain on less nitrogen fertilizer, and to grow more meat on less grain.

In addition to the story N-PRINT tells are studies piling up from Harvard's public health school, the National Cancer Institute and others linking a red meat diet to obesity, cancers and premature death.

So it's simple. By cutting meat consumption by half, and by wasting half as much food — more than one-third of all food produced in the United States is never eaten, according to the U.S. Department of Agriculture — we could dramatically slash nitrogen fertilizer use and pollution to coastal waters like the Chesapeake.

And we'd all be healthier.

The reality, though, is that our history of environmental cleanup is one of employing all manner of good and clever tools, from better sewage treatment technologies to natural buffers between farms and waterways rather than retooling ourselves, the way we live and eat, and stabilizing our population numbers.

We may keep the environment on life support with our toolbox (nitrogen controls on newer vehicles, for example, are the reason there's not a bigger difference between Pave It's SUV and Save It's bicycle). And widespread planting of winter cover crops to suck up runoff from fields could make feeding more than half of our corn to animals for meat less polluting.

But it's going to take more than treating symptoms while ignoring root causes, more than applying "end of pipe" solutions instead of changing polluting processes, to achieve the sustainable environment we say we want.

In the long run, changing polluting processes will probably save taxpayers a lot of money too — simply curtailing government subsidies to everything environmentally harmful, from sprawl development to septic tanks and row cropping corn, would help.

And the powerful intersection of improved human health plus improved water quality that would come from changing our diets — not all that radically either — is something we can no longer ignore.